1. Field of the Invention
The present invention relates to a label printer for printing a given image on a label and issuing the label.
2. Description of Related Art
A label printer of this kind has already been proposed by the present assignee in Japanese Utility Model Application Nos. 3-98205 and 3-98975, for example. Such a label printer will be described with reference to FIGS. 11 to 13. Referring to FIGS. 11 and 12, reference numeral 101 generally designates a label printer having a body housing 102. A printing section 103 and a storing section 104 are provided in the body housing 102 at front and rear portions thereof, respectively. The storing section 104 is adapted to rotatably support a roll of a label sheet 105 (see FIG. 11) or a label sheet 106 (see FIG. 12). The label sheet 105 consists of a continuous base sheet (not shown) and a plurality of labels (not shown) releasably attached to an inside surface of the rolled base sheet, while the label sheet 106 consists of a continuous base sheet (not shown) and a plurality of labels (not shown) releasably attached to an outside surface of the rolled base sheet. The printing section 103 is adapted to print a given image on the labels of the label sheet 105 or 106. The printing section 103 includes a line head 108 pivotably supported at a rear end portion thereof by a support shaft 107, a platen roller 109 located under the line head 108 at a front end portion thereof, and a position holding mechanism (not shown) such as a locking mechanism for releasably pressing the line head 108 against the platen roller 109 and holding such an operative position of the line head 108. As shown in FIG. 13, the body housing 102 is constituted by a lower housing 110 and an upper housing 111 mounted on the lower housing 110 so as to be pivotably supported at a rear end portion thereof. The printing section 103 and the storing section 104 are normally covered with the upper housing 111. A pair of guide plates 113 and 114 are located under the rear end portion of the line head 108. A light emitting element and a light receiving element (neither shown) are mounted in the guide plates 113 and 114, respectively, to constitute a position sensor (not shown) for detecting a position of each label of the label sheet 105 or 106. A label separator 115 for sharply bending the base sheet of the label sheet 105 or 106 to thereby separate each label from the base sheet after printing is located before the platen roller 109. An ejection roller 116 for ejecting the base sheet of the label sheet 105 or 106 after separating each label is located below the platen roller 109 in contact therewith so as to be driven by the platen roller 109.
Although not shown, a sensor is provided before the label separator 115 to detect the presence of the label projecting forward from the label separator 115 after separation of the label from the base sheet. Further, a contact switch (not shown) as a movable member detecting device is located at a position interfering with a part of the line head 108 during pivotal movement of the line head 108 about the support shaft 107, so as to detect the pivotal movement of the line head 108.
In operation, the roll of the label sheet 105 or 106 selectively stored in the storing section 104 is unwound to be fed through the guide plates 113 and 114 to the printing section 103. In the printing section 103, the label of the label sheet 105 or 106 is thermally scanned by the line head 108 as being fed by the platen roller 109 to print a given image on the label. At this time, the position of each label of the label sheet 105 or 106 fed by the platen roller 109 is detected by the position sensor provided in the guide plates 113 and 114 to control operation timing of the line head 108.
After printing the given image on the label attached to the base sheet of the label sheet 105 or 106, the base sheet only is sharply bent by the label separator 115 to separate the label from the base sheet. Then, the base sheet is fed so as to be ejected by the eject roller 116 and the platen roller 109. On the other hand, the label separated from the base sheet is issued so as to project forward from the label separator 115. Alternatively, after printing a given image on the label of the label sheet 105 or 106, the label sheet 105 or 106 may be issued without bending the base sheet and separating the label from the base sheet by means of the label separator 115. At this time, the presence of the label or the label sheet 105 or 106 projecting forward from the label separator 115 after separation is detected by the sensor located before the label separator 115 to thereby control a drive timing of the platen roller 109.
In the case of replacing the label sheet 105 or 106 or removing jamming which has occurred in the label printer 101, the upper housing 111 and the line head 108 are swung upwardly to expose the storing section 104 and the printing section 103 to the outside of the label printer 101. In manually setting the label sheet 105 or 106 into the printing section 103, the label sheet 105 or 106 is first inserted between the guide plates 113 and 114 and then put on the platen roller 109. Then, the base sheet of the label sheet 105 or 106 is inserted between the platen roller 109 and the ejection roller 116. In the condition where the line head 108 is upwardly swung, it is necessary to stop the operation of the printing section 103. In this line printer 101, the upwardly swung condition of the line head 108 is detected by the contact switch to thereby control power supply to the printing section 103.
The sensor for detecting the presence of the label projecting forward from the label separator 115 is constructed of optical means in general. Examples of such an optical sensor in the related art will be described with reference to FIGS. 14 to 17.
FIGS. 14 and 15 show a first example of the optical sensor in the related art. Referring to FIG. 14, reference numeral 4 generally designates a printer having a body housing 1 in which a line head 2 and an eject unit 3 are provided in spaced relationship from each other. Thus, a label issue opening 5 having a predetermined width is defined between the line head 2 and the eject unit 3 at their front ends. A light emitting element 6 is located below the label issue opening 5 on the side near one end of the opening 5, and a light receiving element 7 is located above the label issue opening 5 on the side near the other end of the opening 5 so as to receive light emitted from the light emitting element 6. Accordingly, an optical axis 9 obliquely intersecting a label 8 issued from the label issue opening 5 is formed between the light emitting element 6 and the light receiving element 7.
FIGS. 16 and 17 show a second example of the optical sensor in the related art. In FIGS. 16 and 17, the same reference numerals as those appearing in FIGS. 14 and 15 designate the same parts, and an explanation thereof will be omitted. In this example, a reflective sensor 12 constructed of a light emitting element 10 and a light receiving element 11 in an integral structure is provided over the label issue opening 5 at a central position thereof.
The problems in the above related art will now be described. First, in the label printer 101, the swung condition of the line head 108 is detected by the contact switch, and the power supply to the printing section 103 is controlled according to the detection result from the contact switch. However, the contact switch as the movable member detecting device can merely detect the movement of only one movable member. Accordingly, when there are many movable members whose movements are required to be detected, many movable member detecting devices corresponding to the movable members must accordingly be installed, thus hindering a reduction in size and weight of an equipment and the productivity thereof.
In the first example of the optical sensor shown in FIGS. 14 and 15, detection is possible in the case where the width of the label 8 is large as shown by letter A in FIG. 15. However, the detection is impossible in the case where the width of the label 8 is small as shown by letter B in FIG. 15. Such a defect may be eliminated by offsetting the position of the optical axis 9 intersecting the label 8 toward one end of the label issue opening 5 in the case where an issue reference of the label 8 is set at the one end of the label issue opening 5. However, in the first example, the distance between the light emitting element 6 and the light receiving element 7 is large, so that scattering of the light is apt to occur, thus reducing a reliability of detection.
Further, in the second example of the optical sensor shown in FIGS. 16 and 17, the reflective sensor 12 itself has a diameter of 5.8 mm, and the amount of projection from a mounting surface of the reflective sensor 12 inclusive of its mounting member becomes about 10 mm. Accordingly, in the case that the label 8 is issued from the label issue opening 5 without being separated from the base sheet and that the label 8 issued is cut together with the base sheet by means of a cutter (not shown) located on the downstream side of the reflective sensor 12 in respect of an issuing direction of the label 8, there is a possibility that the reflective sensor 12 will interfere with the label 8 so as to damage the label 8. Further, since the reflective sensor 12 is located at the central position of the label issue opening 5, there arises a problem in manufacture such that electrical wiring to the reflective sensor 12 is difficult so to make the assembly operation hard to accomplish. In addition, since the wiring to the reflective sensor 12 appears outside of the label printer, the appearance of the printer will be spoiled.